That’s according to two new studies that contradict a widely held theory that a comet (or comets) crashed into North America 12,900 years ago. The impact was believed to have triggered the Younger Dryas Period, an era of rapid cooling that saw the extinction of the woolly mammoths, among other species.

Prior to Younger Dryas, ice sheets from the former Ice Age were melting and the planet was almost as warm as it is today. But near-glacial temperatures abruptly returned in a matter of decades — and lasted 1,500 years.

Understanding this mini-Ice Age is key to helping scientists better understand the Earth’s climate system. Does the climate need an extraterrestrial calamity to go berserk? Or is it capable of doing that on its own?

The idea that a massive cosmic impact triggered abrupt climate change was first proposed in 2007, and has remained a contentious debate among scientists. Both papers, published in the Journal of Quaternary Science, challenge evidence cited by supporters of the impact hypothesis. The authors conclude that previous research was either misjudged or interpreted with bias.

One study found no evidence of a spike in the levels of impact-derived “nanodiamonds” in sediment layers from Younger Dryas. The authors also concluded that earlier researchers erred in identifying the presence of lonsdaleite, a rare type of diamond formed out of impact — such as a meteor crashing into Earth.

“There’s no lonsdaleite in these sediments, no lonsdaleite whatsoever,” said Tyrone Daulton, lead author of the second paper. He admitted that the presence of lonsdaleite would suggest something interesting but that “it’s all been misidentified.”

The second paper found that paleofire evidence was misinterpreted to show that an impact caused massive wildfires across North America at the onset of Younger Dryas.

“The idea of a Younger Dryas impact was an interesting one,” Andrew Scott, lead author of one of the papers, said in a statement. “However, increasingly methodological research over the past few years has failed to corroborate that story.”